The present invention relates to an image forming system including a copier, printer and fax machine to form color images based on electrophotographic technology.
Electrophotographic technology involves the formation of a static latent image corresponding to image data on a photoconductor, after which electrically charged toner particles are deposited on the photoconductor corresponding to the potential pattern of the static latent image, thereby visualizing the latent image as a toner image. Then, this toner image is transferred onto a recording medium, such as paper, to form an image on the paper. If a color image is to be formed in this process, toner of multiple colors, for example, yellow, magenta and cyan, must be superimposed to form the color image.
An image forming system to form color images is variously characterized by the method of superimposing toner particles of different colors. Proposed color image forming methods can be broadly classified into two types: a repeated development method where toner of various colors is developed repeatedly on one photoconductor to produce color images, and a simultaneous development method where toner particles of various colors are developed on multiple photoconductors simultaneously to produce color images. The following describes the details of various color image forming methods will be described.
In the repeated development method, one photoconductor is used to form a color image. This method includes the following three methods: photoconductor color superimposition transfer drum and intermediate transfer.
Of these methods, an intermediate transfer method capable of recording high quality pictures is disclosed in Japanese Patent Laid-Open No. 137179/1996, where multiple development devices which develop different color toner particles around the photoconductor and an intermediate transfer device are arranged so that the toner image formed on the photoconductor is transferred on the intermediate transfer device. This is repeated for each color, so that toner particles of multiple colors are superimposed on the intermediate transfer device. After that, the toner image on the intermediate transfer device is transferred onto paper, thereby producing a color image.
The simultaneous development method is disclosed in Japanese Patent Laid-Open No. 186894/1998 and Japanese Patent Laid-Open No. 260593/1998, for example. This method uses multiple photoconductors, and toner images are formed simultaneously by each photoconductor. Toner images are transferred synchronously with paper feed, thereby forming color images. This color image forming method is also called the tandem method and is typical of the simultaneous development method.
Increasing use of colors and digital data in office environments has resulted in a growing demand for color images to be printed on recording media, such as paper. A color image forming system to meet this demand is required to satisfy the following four performance requirements: (1) compact configuration to allow installation at limited space installation site in an office, (2) high picture quality to produce photo outputs, (3) compatibility with a great variety of recording media such as the OHP and cardboards in addition to plain paper, and (4) high speed to ensure that a great volume of business documents can be printed in a limited time.
Of these, two requirementsxe2x80x94(1) compact configuration which is a prerequisite for office installation and (2) high speed printing resulting from color image processing technology and high speed transmission technology supported by technologically advanced PCs and networksxe2x80x94are important performance requirements which are essential to the subsequent color image forming systems.
The tandem method introduced above facilitates this speed increase. This method forms toner images of various colors almost simultaneously. It allows color images to be formed at the same speed as that of the monochrome printer. However, images are created independently for each photoconductor, and this makes it very difficult to superimpose toner images of various colors. Registration of toner images of various colors depends on the layout accuracy of each photoconductor and the exposure device, such as pitch and parallelism. If they are not laid out with high accuracy, the picture quality will be subsequently deteriorated; for example, variations of hues, a double image or other troubles will result from misregistration of toner images of different colors Furthermore, this layout accuracy will be subsequently reduced when the user mounts or removes the consumable photoconductor at the time of replacement. When the tandem method is used, registration of toner images of different colors poses a serious problem if recording of high picture quality is to be ensured.
One object of the present invention is to provide a compact and high-speed image forming system which ensures recording of high picture quality.
Another object of the present invention is to provide a image forming system characterized by excellent maintainability.
An image forming system according to the present invention comprises multiple photoconductors, multiple exposure devices to form static latent images on each of said photoconductors, multiple development devices to form toner images on each of said photoconductors, an intermediate transfer device to form a color toner image by superimposing said toner images, a transfer device to transfer said color toner image to a recording medium, and a fusing device to fuse said color toner image on said recording medium; wherein said multiple photoconductors form one integral unit.
A photoconductor unit has multiple photoconductors arranged in a line, multiple charging devices to charge each of said photoconductors uniformly, and multiple photoconductor cleaners to clean each of said multiple photoconductors. Said multiple photoconductors, multiple charging devices and multiple photoconductor cleaners are configured in one unit.
Since multiple photoconductors are used for printing, higher printing speed is ensured than that obtained when only one photoconductor is used. Multiple photoconductors configured in one unit eliminate the possibility of displacement of photoconductors during mounting and dismounting at the time of replacement. Recording with a high picture quality is ensured without image misregistration during printing. Maintainability is also improved at the same time.
Furthermore, another image forming system according to the present invention comprises multiple photoconductors arranged in a longitudinal line, multiple development devices and multiple exposure devices arranged on one side of said multiple photoconductors, an intermediate transfer device arranged on the other side of said multiple photoconductors, and a form cassette arranged below said multiple photoconductors; wherein said multiple development devices and multiple exposure devices are arranged in the vertical direction relative to said multiple photoconductors, and said multiple development devices and multiple exposure devices are arranged alternately with respect to the direction of said multiple photoconductors.
Such a layout configuration allows for high speed printing despite use of multiple photoconductors. This permits a compact image forming system to be provided.
Fixing the exposure devices on the enclosure side of the image forming system eliminates the possibility of design-based misregistration of exposure. This makes it possible to provide an image forming system characterized by a stable exposure and high quality image recording.